Expression of Dopamine Receptor 1A and Cannabinoid Receptor 1 Genes in the Cochlea and Brain after Salicylate-Induced Tinnitus.

The purpose of this study was to investigate the mRNA expression of the dopamine receptor 1A (DR1A) and cannabinoid receptor 1 (CR1) genes in mice with tinnitus. Sixteen 3-month-old male SAMP8 mice were randomly and equally divided into two groups (8 mice in each group): a control (saline-treated) group and a tinnitus (salicylate-treated) group. The mRNA expression of the DR1A and CR1 genes in the cochleae and brains of the mice was evaluated after tinnitus had been induced by intraperitoneal injection of sodium salicylate (300 mg/kg body weight). The results showed that 4-day salicylate treatment (unlike 4-day saline treatment) caused a significant increase in the tinnitus score and in mRNA expression of the DR1A gene in the cochlea, the brainstem and inferior colliculus, the hippocampus and parahippocampus, and the temporal lobe, but not the frontal lobe. Conversely, 4-day salicylate treatment caused significantly lower mRNA expression of the CR1 gene in the cochlea and all the brain areas tested. In summary, salicylate-induced tinnitus may be associated with increased mRNA expression of the DR1A gene - but with decreased mRNA expression of the CR1 gene - in the cochlea and in many tinnitus-related brain areas.